Static reducer for wireless signals



A. M. CURTIS.

STATIC REDUCER FOR WIRELESS SIGNALS.

APPLICATION FILED NOV. 1, I916- 1A1 5,999 Patented May1 6,'1922.w

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AUSTEN M. CURTIS, OF BROOKLYN. NEW YORK. ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED. OF NEW YORK. N. Y.. A CORPORATION OF NEW YORK.

STATIC BEDUCER FOR WIRELESS SIGNALS.

Specification of Letters Patent.

Patented May 16. 1922.

Application filed November 1, 1916. Serial No. 128,881.

To a]? 10710712 2'! may concern Be it known that I. Atsrnx M. CURTIS. a citizen of the Ynited States. residing at Brooklyn. in the county of Kings and Stateof New York. have invented certain new and useful Improvements in Static Reducers for 'ireless Signals. of which the following is a full. clear. concise. and exact description.

This invention relates to the class of soealled detectors of electromagnetic wave energy which are direct translators of such e11- ergy and possess the property of changing oscillating current energy into a series of unidirectional impulses. The object of this invention is'to furnish 1n a receiving system of electromagnetic wave energy. a detector capable of strongly reducing all strong incidentwave impulses interfering with the proper reception of the desired signals.

A. further object is to furnish an asymmetric device that will efficiently rectify relativelyweak alternating impulses and will rectify relatively strong alternating impulses much less efiiciently.

It is well-known in practice that electric currents or oscillations materially stronger than those of the desired signals. such as static and atmospheric disturbances. seriously afi'ect the ability of the operator to read the desired signals. If. in addition to the desired signals. still other signals are incident upon the detector. these also may be a source of disturbance. especially if their sending station is .in close proximity to the detector so as to make them of appreciable strength. This invention avoids such interference by having the rectifier so constructed that it will be practically non-rectifying for strong interfering impulses. I

It has been found that various crystalline materials which act as rectifiers of alternating currents have the additional property of losing much of their rectifying action when the lmpressed oscillations become strong. This has been found to be particularly true of certain carborundum crystals and use is made of this fact to accomplish the objectsrundum-to-metal contact; and Figure 3 illustrates how this invention may be used in an ordinary wireless receiving system.

The usual carborundum-to-metal contact rectifier. such as is used for wireless signaling. has a characteristic curve similar to Figure 2. in which its resistance R in ohms is plotted against the corresponding impressed voltages V. From the curve it may be seen that for all alternating voltages over the working range. the resistance values are asymmetrical. If. for example. the alternating voltage has a value of one volt. for a positive voltage oft-hat value. the rectifier has a resistance of 750,000 ohms approximately. But for a negative voltage of the same amount. the resistance is about 3,500,000 ohms. Even when the alternating voltage is as high as three volts. the value of the resistance for the negative voltage is over twice as large as for the positive value. The same inequality of resistance holds for all other values of the voltage. Hence, arectifier possessing such a characteristic curve will have an asymmetrical currentflowing through it for all impressed alternating voltages over the working range. Consequently. such a rectifier will not eliminate strong interfering impulses. but will rectify them as well as the desired signals.

But by experiment it is possible to select a carborundum-to-metal contact that has a. characteristic curve similar to Figure 1 in which we have symmetrical resistance for large impressed voltages but asymmetrcial for low voltages. If. for example. the instantaneous impressed alternating voltage is three volts. the positive and negative values of the resistance are very nearly the same. namely. 119.000 ohms for the positive value and 120.000 ohms for the negative value. But if the instantaneous voltage is'small. sav 0.5 of a volt. there is asynmietry of resistance. the positive value being 300.000 ohms and the negative value 200.000 ohms. 100 In the first case. there can be no rectification over the portion of the voltage wave which gives equal resistance values for both polarities. 'hat little rectification does occur will be for that fraction of the voltage wave 105 in which the voltage values are all below the minimum value for symmetrical resistance values; if the instantaneous value is large. as illustrated by the first'example. that part of the voltage wave which does give rectifica- 110 tion will be only a small fraction of the total wave, so that what rectification does occur may be said to very inefiicient. But impressed signals of smaller voltage values would be rectified during the complete cycle. as is shown by the latter mentioned case. Thus, if a small alternating voltage is impressed on a contact of this class, there will. in general, be rectification dependent for its amount on the polarizing voltage; but for alternating voltages high enough to bring the resistance down to the point where it becomes constant and equal for both polarities. the rectification will be relatively much smaller. By a suitable adjustment of a rectifier containing a carborundum-to-metal contact of this type. it is possible to cause relatively strong undesired signals to be very much reduced in most cases. while not affecting materially the strength of the weak signals that are to be read.

One of the ways in which this characteristic of particular crystal contacts may be employed is shown in Figure 3. Assume that the energy received by the antenna 4 consists of strong static impulses and the weaker signals that are to be read. It may be found desirable to amplify the signals in order to get them to the desired strength for good rectification. In such a case. a. high frequency amplifier 5 of any desired form. such as the audion amplifier, may be used in a manner well-known in the art. This system will give equal amplification for both kinds of energy received from the antenna. After amplification, the energy is impressed on tuned circuit 6. and then passed on to the tuned circuit 7, containing the carborundum-to-metal rectifier 8 of the type herein described. Owing to its symmetrical characteristic curve for high alternating voltages. the carborundum-to-metal contact will not be unilaterally conductive for them; for the high frequency voltage in one direction will produce about the same amount of current as when the voltage is reversed. thereby producing little rectification. The rectifier. however, will rectify the weak signals efficiently, owing to its characteristic curve being asymmetrical for low alternating voltages as heretofore explained.

The unidirectional impulses resulting from the rectification of the low frequency signals pass through the inductance 11, and are impressed on the input circuit of an amplifier 14 of any desired type. such as the audion amplifier. In the output circuit of said amplifier. there is a receiver 15 suitable for reading the amplified signals. In order to produce the desired effect. it may sometimes be found necessary to use a polarizing voltage for the rectifier supplied from the battery 10, which can be so adjusted that the impulses incident on the rectifier cause it to work with more exactness on that part of 'ances and desired signals.

tification for the static oscillations but recti-v fies the desired signals. Circuits 6 and T may be tuned to any desired frequency by means of condensers 12 and 13. Circuit 6 is inserted in the system to aid in the sharper tuning of the circuit containing the rectifier.

It makes no difference whether the strong interfering signals are atmospheric, static or interfering spark signals of any degree of damping. Suitable adjustment of the polarizing "oltages will reduce the louder signals very much. so that the weak signals may be read through the strong interference.

Although a carborundum-to-nietal contacthas been described as representative of this invention, it is to beunderstood that the invention is not limited to such a rectifier, but applies to any rectifier which possesses a characteristic such as shown in Figure 1.

While the crystals which possess the desired properties cannot be selected by external appearance. they can readily be assorted by simple itxperimental tests.

It is to be understood that the particular form of receiving circuit shown in Figure 3 is not essential; but that many changes may be made therein without in any manner affecting the operativeness of the crystal rectifier to distinguish between strong disturb- For example the amplifiers 5 and H may be omitted and the various arrangements of tuned circuits may be altered to suit the particular conditions at any given station.

What is claimed is:

1. A detector for electromagnetic waves consisting of a single rectifying device which has a non-uniform conductive path whose characteristic curve is asymmetrical for the lower voltages of the order used to givesignal indications in electromagnetic wave receiving stations and symmetrical for all voltages of materially higher orders.

2. A detector for electromagnetic waves comprising a single rectifying device having a conductive path possessing asymmetrical resistance values for the lower voltages of the order used to give signal indications in electromagnetic wave receiving stations, but symmetrical resistance values for all voltages of a materially higher order.

3. A detector of electromagnetic waves comprising a carborundum-to-metal contact possessing a characteristic resistance curve asymmetrical for low voltages but symmetrical and equal for relatively high voltages.

4:. In wireless telegraph a detector comprising that form of carborundum which has a characteristic curve symmetrical about the resistance axis for relatively large voltages but asymmetrical for relatively small voltages.

5. A rectifier for alternating current comprising two conducting solid elements in contact, the characteristic of said detector being symmerical for high voltages but asymmetrical for 10w voltages.

6. A rectifier for alternating current including a conductor possessing, when unenergized by undirectional current, asymmetrical resistance values for the lower values of voltages used to give signal indications in electromagnetic Wave receiving stations but symmetrical resistance values for the higher values of voltages which will give signal indications in such stations.

7. A rectifier for alternating current in? cluding one solid and another metallic element in contact, the characteristic of said rectifier being symmetrical for high voltages but asymmetrical for low voltages.

8. A rectifier for alternating current including tWo elements in continuous physical 10. A detector for alternating current 4 comprising a single unsymmetrically conductin path, the characteristic of said detector eing symmetrical for high voltages but gradually and continuously becoming asymmetrical as the voltage decreases.

In Witness whereof, I hereunto subscribe my name this 30th day of October A. D.,

AUSTEN M. CURTIS. 

